im_instance_conf fails randomly.


mysql-test/r/im_options.result:
  Updated result file.
mysql-test/t/im_instance_conf.imtest:
  Added a note about specific of CREATE INSTANCE usage in IM-tests.
mysql-test/t/im_options.imtest:
  1. Specify socket-file-name for new instance so that the test
     does not depend on another running test-suite on the same box.
  2. Added a note about specific of CREATE INSTANCE usage in IM-tests.